A humid continental climate is a climatic region typified by large seasonal temperature differences, with warm to hot (and often humid) summers and cold (sometimes severely cold) winters. Precipitation is relatively well distributed year-round in many areas with this climate, while others may see a marked reduction in wintry precipitation and even a wintertime drought. Snowfall, regardless of average seasonal totals, occurs in all areas with a humid continental climate and in many such places is more common than rain during the height of winter. In places with sufficient wintertime precipitation, the snow cover is often deep. Most summer rainfall occurs during thunderstorms and a very occasional tropical system. Though humidity levels are often high in locations with humid continental climates, it is important to note that the "humid" designation does not mean that the humidity levels are necessarily high, but that the climate is not dry enough to be classified as semi-arid or arid.

The average temperature for the year in New Castle is 51.0°F (10.6°C). The warmest month, on average, is July with an average temperature of 74.0°F (23.3°C). The coolest month on average is January, with an average temperature of 29.0°F (-1.7°C).

The highest recorded temperature in New Castle is 101.0°F (38.3°C), which was recorded in July. The lowest recorded temperature in New Castle is -19.0°F (-28.3°C), which was recorded in February.

The average amount of precipitation for the year in New Castle is 39.4" (1000.8 mm). The month with the most precipitation on average is June with 4.9" (124.5 mm) of precipitation. The month with the least precipitation on average is October with an average of 2.3" (58.4 mm). In terms of liquid precipitation, there are an average of 70.7 days of rain, with the most rain occurring in June with 7.7 days of rain, and the least rain occurring in October with 4.0 days of rain.